FGLinearActuator Class Reference

Detailed Description

Models a flight control system summing component.

Linear actuators typically operate by conversion of rotary motion into linear motion. The linear_actuator component is described in the Wikipedia link: https://en.wikipedia.org/wiki/Linear_actuator.

Linear actuators converts a rotation into a linear movement or a multiturn rotation. For the conversion it is necessary to declare a module that is defined by the difference of the maximum and minimum value Input.

List of parameters:

• input: Value to be transformed
• Output: Output value following the following rule it is the result of gain * (bias + Input + module*countSpin)
• CountSpin is the number of complete rotations calculated by this device
• gain: Apply a multiplication coefficient to the output value, the default value is 1.0
• bias: Value that is added to the input value
• module: Difference between the maximum and minimum value of Input. Default is 1.0.
• hysteresis: Defines the sensitivity of the actuator according to the input.

For example, if the actuator has a module of 360 and if the hysteresis is 5.0, the actuator, with gain = 1, will output a value equal to: 5, 10...355, 360, 365, 370 etc. This parameter allows to simulate stepper motors. The default value is 0.1 It is not advisable to have this parameter too small (less than 0.1) as it could make the CPU load heavier.

• versus: Direction of rotation if fixed. The versus allows to obtain a mechanism similar to the tick of a clock. The default value is 0.

If the value is zero, the verse is automatically obtained according to variation of the input data.

If set to a value > 0.5 the verse is increasing, i.e. the output changes only if the Input value is greater than the previous one.

If set to a value < -0.5 the output is changed only if the next value is lower than the previous one.

With this parameter allows to easily obtain a "step counter".

• rate: To define when the rotation is complete, the differential criterion is used.

For example, if the rotation is clockwise and the module is 360, the revolution will be complete when the input value changes from 360 to 0.

When this happens a counter increases the output of the value of the module. As a way the system keeps track of the number of rotations. Rate defines the sensitivity of the system.

If a difficulty in determining the rotation is observed during the tests, this parameter must be modified with a positive value not exceeding 1. The default value is 0.3

• set: If the absolute value is greater or equal 0.5, the output changes according to the input.

If its value is lower 0.5, the output remains constant (the system stores the data). The use of this parameter allows to simulate the behavior of a servomechanism that is blocked, for example due to a power failure.

• Reset: if the absolute value is greater or equal 0.5, the output returns to zero and reset internal data.
• lag: Activate a lag filter on exit if the value is greater 0.0 the lag is active.

Be very careful to use the lag filter in case you use two or more "linear_actuator" in cascade; it may happen that the smoothing effect due to the lag in the output value can mislead the rotation determination system. The effect is similar to that of a loose coupling of a rack and pinion. Therefore, with these types of coupling, place lag only at the last stage.

<linear_actuator name="{string}">
  <input> {property name} </input>
  <bias> {property name | value} </bias>
  <module> {value} </module>
  <hysteresis> {value} </hysteresis>
  <rate> {value} </rate>
  <versus> {property name | value} </versus>
  <gain> {value} </gain>
  <set> {property name | value} </set>
  <reset> {property name | value} </reset>
  <lag> {value} </lag>
  <output> {property name} </output>
</linear_actuator>

Mechanical counter:

It is the typical mechanism used to count the kilometers traveled by a car, for example the value of the digit changes quickly at the beginning of the km. Module 10 indicates that the count goes from 0 to 9 after one complete revolution.

<linear_actuator name="systems/gauges/PHI/indicator/digit3AW">
  <input>systems/gauges/PHI/indicator/digit3A</input>
  <module>10</module>
  <rate>0.2</rate>
  <lag>8.0</lag>
</linear_actuator>

The gyrocompass from a rotation with a value from 0 to 259 degrees. When it returns to zero, if it is made more realistic by means of an actuator, there is a jump of the disk which performs a complete rotation of 360 °. By activating a linear actuator followed by an actuator it is possible to obtain a very realistic result.

<linear_actuator name="gyrocompass-magnetic-deg-linear">
  <input>gyrocompass-magnetic-deg</input>
  <module>360</module>
</linear_actuator>
 
<actuator name="gyrocompass-magnetic-deg-linear-actuator">
  <input>gyrocompass-magnetic-deg-linear</input>
  <lag>2.0</lag>
  <rate_limit>100</rate_limit>
  <bias>0.1</bias>
  <deadband_width>1</deadband_width>
  <hysteresis_width>0.5</hysteresis_width>
</actuator>

Count steps with memory:

If you use a button or switch to advance a mechanism, we can build a step counter. In this case the module is 1 and the rate 1. The verse is positive (increasing). A pulse counter (for example the count of the switched-on states of a switch with values 1 and 0), the module must be 1 in that each step must advance its value by one unit. The verse is "1" because it has to accept only increasing values (as in a clock escapement). The gain is 0.5 because, in similitude to an escapement of a clock, the gear makes two steps for a complete rotation of the pendulum.

<linear_actuator name="systems/gauges/PHI/doppler/switch-increase-summer">
  <input>systems/gauges/PHI/doppler/switch-increase</input>
  <module>1</module>
  <rate>1</rate>
  <versus>1</versus>
  <gain>0.5</gain>
  <lag>0.0</lag>
  <reset>systems/gauges/PHI/doppler/test_reset_off</reset>
</linear_actuator>

Author

Adriano Bassignana

Definition at line 220 of file FGLinearActuator.h.

#include <FGLinearActuator.h>

Inheritance diagram for FGLinearActuator:

Collaboration diagram for FGLinearActuator:

Public Member Functions
	FGLinearActuator (FGFCS *fcs, Element *element)
	Constructor.
	~FGLinearActuator ()
	Destructor.
bool	Run (void) override
	The execution method for this FCS component.
Public Member Functions inherited from FGFCSComponent
	FGFCSComponent (FGFCS *fcs, Element *el)
	Constructor.
virtual	~FGFCSComponent ()
	Destructor.
std::string	GetName (void) const
double	GetOutput (void) const
virtual double	GetOutputPct (void) const
std::string	GetType (void) const
virtual void	ResetPastStates (void)
virtual void	SetOutput (void)
Public Member Functions inherited from FGJSBBase
	FGJSBBase ()
	Constructor for FGJSBBase.
virtual	~FGJSBBase ()
	Destructor for FGJSBBase.
void	disableHighLighting (void)
	Disables highlighting in the console output.

Additional Inherited Members
Public Types inherited from FGJSBBase
enum	{ eL = 1 , eM , eN }
	Moments L, M, N. More...
enum	{ eP = 1 , eQ , eR }
	Rates P, Q, R. More...
enum	{ eU = 1 , eV , eW }
	Velocities U, V, W. More...
enum	{ eX = 1 , eY , eZ }
	Positions X, Y, Z. More...
enum	{ ePhi = 1 , eTht , ePsi }
	Euler angles Phi, Theta, Psi. More...
enum	{ eDrag = 1 , eSide , eLift }
	Stability axis forces, Drag, Side force, Lift. More...
enum	{ eRoll = 1 , ePitch , eYaw }
	Local frame orientation Roll, Pitch, Yaw. More...
enum	{ eNorth = 1 , eEast , eDown }
	Local frame position North, East, Down. More...
enum	{ eLat = 1 , eLong , eRad }
	Locations Radius, Latitude, Longitude. More...
enum	{   inNone = 0 , inDegrees , inRadians , inMeters ,   inFeet }
	Conversion specifiers. More...
Static Public Member Functions inherited from FGJSBBase
static const std::string &	GetVersion (void)
	Returns the version number of JSBSim.
static constexpr double	KelvinToFahrenheit (double kelvin)
	Converts from degrees Kelvin to degrees Fahrenheit.
static constexpr double	CelsiusToRankine (double celsius)
	Converts from degrees Celsius to degrees Rankine.
static constexpr double	RankineToCelsius (double rankine)
	Converts from degrees Rankine to degrees Celsius.
static constexpr double	KelvinToRankine (double kelvin)
	Converts from degrees Kelvin to degrees Rankine.
static constexpr double	RankineToKelvin (double rankine)
	Converts from degrees Rankine to degrees Kelvin.
static constexpr double	FahrenheitToCelsius (double fahrenheit)
	Converts from degrees Fahrenheit to degrees Celsius.
static constexpr double	CelsiusToFahrenheit (double celsius)
	Converts from degrees Celsius to degrees Fahrenheit.
static constexpr double	CelsiusToKelvin (double celsius)
	Converts from degrees Celsius to degrees Kelvin.
static constexpr double	KelvinToCelsius (double kelvin)
	Converts from degrees Kelvin to degrees Celsius.
static constexpr double	FeetToMeters (double measure)
	Converts from feet to meters.
static bool	EqualToRoundoff (double a, double b)
	Finite precision comparison.
static bool	EqualToRoundoff (float a, float b)
	Finite precision comparison.
static bool	EqualToRoundoff (float a, double b)
	Finite precision comparison.
static bool	EqualToRoundoff (double a, float b)
	Finite precision comparison.
static constexpr double	Constrain (double min, double value, double max)
	Constrain a value between a minimum and a maximum value.
static constexpr double	sign (double num)
Static Public Attributes inherited from FGJSBBase
static char	highint [5] = {27, '[', '1', 'm', '\0' }
	highlights text
static char	halfint [5] = {27, '[', '2', 'm', '\0' }
	low intensity text
static char	normint [6] = {27, '[', '2', '2', 'm', '\0' }
	normal intensity text
static char	reset [5] = {27, '[', '0', 'm', '\0' }
	resets text properties
static char	underon [5] = {27, '[', '4', 'm', '\0' }
	underlines text
static char	underoff [6] = {27, '[', '2', '4', 'm', '\0' }
	underline off
static char	fgblue [6] = {27, '[', '3', '4', 'm', '\0' }
	blue text
static char	fgcyan [6] = {27, '[', '3', '6', 'm', '\0' }
	cyan text
static char	fgred [6] = {27, '[', '3', '1', 'm', '\0' }
	red text
static char	fggreen [6] = {27, '[', '3', '2', 'm', '\0' }
	green text
static char	fgdef [6] = {27, '[', '3', '9', 'm', '\0' }
	default text
static short	debug_lvl = 1
Protected Member Functions inherited from FGFCSComponent
virtual void	bind (Element *el, FGPropertyManager *pm)
void	CheckInputNodes (size_t MinNodes, size_t MaxNodes, Element *el)
void	Clip (void)
void	Delay (void)
Static Protected Member Functions inherited from FGJSBBase
static std::string	CreateIndexedPropertyName (const std::string &Property, int index)
Protected Attributes inherited from FGFCSComponent
bool	clip
FGParameter_ptr	ClipMax
FGParameter_ptr	ClipMin
bool	cyclic_clip
unsigned int	delay
double	delay_time
double	dt
FGFCS *	fcs
int	index
std::vector< FGPropertyValue_ptr >	InitNodes
double	Input
std::vector< FGPropertyValue_ptr >	InputNodes
std::string	Name
double	Output
std::vector< double >	output_array
std::vector< FGPropertyNode_ptr >	OutputNodes
std::string	Type
Static Protected Attributes inherited from FGJSBBase
static constexpr double	radtodeg = 180. / M_PI
static constexpr double	degtorad = M_PI / 180.
static constexpr double	hptoftlbssec = 550.0
static constexpr double	psftoinhg = 0.014138
static constexpr double	psftopa = 47.88
static constexpr double	fttom = 0.3048
static constexpr double	ktstofps = 1852./(3600*fttom)
static constexpr double	fpstokts = 1.0 / ktstofps
static constexpr double	inchtoft = 1.0/12.0
static constexpr double	m3toft3 = 1.0/(fttom*fttom*fttom)
static constexpr double	in3tom3 = inchtoft*inchtoft*inchtoft/m3toft3
static constexpr double	inhgtopa = 3386.38
static constexpr double	slugtolb = 32.174049
	Note that definition of lbtoslug by the inverse of slugtolb and not to a different constant you can also get from some tables will make lbtoslug*slugtolb == 1 up to the magnitude of roundoff.
static constexpr double	lbtoslug = 1.0/slugtolb
static constexpr double	kgtolb = 2.20462
static constexpr double	kgtoslug = 0.06852168
static const std::string	needed_cfg_version = "2.0"
static const std::string	JSBSim_version = JSBSIM_VERSION " " __DATE__ " " __TIME__

Constructor & Destructor Documentation

FGLinearActuator()

FGLinearActuator	(	FGFCS *	fcs,
		Element *	element
	)

Constructor.

Parameters

fcs	a pointer to the parent FGFCS object.
element	a pointer to the configuration file node.

Definition at line 52 of file FGLinearActuator.cpp.

  : FGFCSComponent(fcs, element)
{
  CheckInputNodes(1, 1, element);
 
  ptrSet = nullptr;
  auto PropertyManager = fcs->GetPropertyManager();
  if (element->FindElement("set")) {
    string property_string = element->FindElementValue("set");
    ptrSet = new FGParameterValue(property_string, PropertyManager, element);
    if (ptrSet && ptrSet->IsConstant()) {
      set = ptrSet->GetValue() >= 0.5;
    }
  }
 
  ptrReset = nullptr;
  if (element->FindElement("reset")) {
    string property_string = element->FindElementValue("reset");
    ptrReset = new FGParameterValue(property_string, PropertyManager, element);
    if (ptrReset && ptrReset->IsConstant()) {
      reset = ptrReset->GetValue() >= 0.5;
    }
  }
 
  ptrVersus = nullptr;
  if (element->FindElement("versus")) {
    string property_string = element->FindElementValue("versus");
    ptrVersus = new FGParameterValue(property_string, PropertyManager, element);
    if (ptrVersus && ptrVersus->IsConstant()) {
      versus = ptrVersus->GetValue();
    }
  }
 
  ptrBias = nullptr;
  if (element->FindElement("bias")) {
    string property_string = element->FindElementValue("bias");
    ptrBias = new FGParameterValue(property_string, PropertyManager, element);
    if (ptrBias && ptrBias->IsConstant()) {
      bias = ptrBias->GetValue();
    }
  }
 
  if (element->FindElement("module")) {
    module = element->FindElementValueAsNumber("module");
    if (module < 0) {
      cout << "FGLinearActuator::Run " << InputNodes[0]->GetNameWithSign()
           << " <module> parameter is forced from " << module
           << " value to 1.0 value" << endl;
      module = 1.0;
    }
  }
 
  if (element->FindElement("hysteresis")) {
    hysteresis = element->FindElementValueAsNumber("hysteresis");
    if (hysteresis < 0) {
      cout << "FGLinearActuator::Run " << InputNodes[0]->GetNameWithSign()
           << " <hysteresis> parameter is forced from " << hysteresis
           << " value to 0.0 value" << endl;
      hysteresis = 0.0;
    }
  }
 
  if (element->FindElement("lag")) {
    lag = element->FindElementValueAsNumber("lag");
    if (lag > 0.0) {
      double denom = 2.00 + dt*lag;
      ca = dt * lag / denom;
      cb = (2.00 - dt * lag) / denom;
      previousLagInput = previousLagOutput = 0.0;
    } else {
      if (lag < 0) {
        cout << "FGLinearActuator::Run " << InputNodes[0]->GetNameWithSign()
             << " <lag> parameter is forced from "
             << lag << " value to 0.0 value" << endl;
        lag = 0;
      }
    }
  }
 
  if (element->FindElement("rate")) {
    rate = element->FindElementValueAsNumber("rate");
    if (rate <= 0 || rate > 1.0) {
      cout << "FGLinearActuator::Run " << InputNodes[0]->GetNameWithSign()
           << " <rate> parameter is forced from " << rate
           << " value to 0.5 value" << endl;
      rate = 0.5;
    }
  }
 
  if (element->FindElement("gain"))
    gain = element->FindElementValueAsNumber("gain");
 
  bind(element, PropertyManager.get());
 
  Debug(0);
}

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~FGLinearActuator()

~FGLinearActuator

(

)

Destructor.

Definition at line 151 of file FGLinearActuator.cpp.

{
  Debug(1);
}

Member Function Documentation

Run()

bool Run ( void  )

overridevirtual

The execution method for this FCS component.

Reimplemented from FGFCSComponent.

Definition at line 158 of file FGLinearActuator.cpp.

{
  if (ptrSet && !ptrSet->IsConstant()) set = ptrSet->GetValue() >= 0.5;
  if (ptrReset && !ptrReset->IsConstant()) reset = ptrReset->GetValue() >= 0.5;
 
  if (reset) {
    inputMem = 0.0;
    countSpin = 0;
    direction = 0;
    Output = 0.0;
    inputLast = 0.0;
  } else {
    if (set) {
      Input = InputNodes[0]->getDoubleValue() - inputLast;
      double inputDelta = Input - inputMem;
      if (abs(inputDelta) >= hysteresis) {
        if (ptrVersus && !ptrVersus->IsConstant()) {
          versus = ptrVersus->GetValue();
          if (versus >= 0.5) {
            versus = 1;
          } else if (versus <= -0.5) {
            versus = -1;
          } else versus = 0;
        }
        if (abs(inputDelta) <= (module * rate)) {
          if (inputDelta > 0.0) {
            direction = 1;
          } else if (inputDelta < 0.0) {
            direction = -1;
          }
        }
        if ((versus == 0) || (versus == direction)) {
          inputMem = Input;
          if (abs(inputDelta) >= (module*rate)) {
            if (inputDelta < 0)
              countSpin++;
            else
              countSpin--;
          }
        } else if ((versus != 0) && (direction != 0) && (versus != direction)) {
          inputLast += inputDelta;
        }
      }
    }
    if (ptrBias && !ptrBias->IsConstant()) {
      bias = ptrBias->GetValue();
    }
    Output = gain * (bias + inputMem + module*countSpin);
  }
 
  if (lag > 0.0) {
    double input = Output;
    Output = ca * (input + previousLagInput) + previousLagOutput * cb;
    previousLagInput = input;
    previousLagOutput = Output;
  }
 
  SetOutput();
 
  return true;
}

---

The documentation for this class was generated from the following files:

• FGLinearActuator.h
• FGLinearActuator.cpp